Astronomical tuning of the La Vedova High Cliff Section (Ancona, Italy) - Implications of the Middle Miocene Climate Transition for Mediterranean sapropel formation

Abstract

Continuous marine successions covering the Middle Miocene Climate Transition (MMCT; -15-13.7 Ma) are scarce and the lack of a high-resolution magnetobiostratigraphic framework hampers the construction of astronomically tuned age models for this time interval. The La Vedova High Cliff section, exposed aiong the coast of the Cònero Riviera near Ancona (Italy), is one of the few Mediterranean sections covering the critica1 time interval of the MMCT. Starting from an initial magnetobiostratigraphic age model, a robust astronomica1 tuning was constructed for the intewal between 14.2 and 13.5 Ma, using geochemical element data and time series analysis. A shift in 6180 of bulk sediment occurs between -13.92 and 13.78 Ma and can be related to the Mi3b oxygen isotope event, reflecting the rapid expansion of the East Antarctic Ice Sheet in the Middle Miocene. The onset of the 6°C CM6 carbon excursion is dated at -13.86 Ma. OUr results confirm the proposition that these events coincide with a 405-kyr minimum in eccentricity and a node in obliquity related t0 the -1.2 Myr cycle. From 13.8 Ma onwards, distinct quadruplet cycles containing sapropelitic sediments are observed, suggesting a causa1 connection between the main Middle Miocene cooling step and sedimentation and circulation in the Mediterranean.